Brain abnormalities blamed for attention deficit disorder

Attention deficit hyperactivity disorder (ADHD), a little-understood condition that affects children, has been pinned to abnormalities in key parts of the brain's prefrontal cortex.

In the first large study to map cerebral areas that have been linked to ADHD, US doctors found that in children with this problem two parts of the brain known as the dorsal prefrontal and anterior temporal regions of the cortex were smaller than they should normally be.

Two other zones, known as enlarged posterior temporal and inferior parietal cortices, were larger.

These are strongly inter-connected parts of the brain that help to process working memory, figure out time and inhibit impulses.

The findings suggest "this action-attentional network is anatomically disrupted in children who have attention-deficit hyperactivity disorder," the researchers report in next Saturday's issue of the British medical weekly The Lancet.

Twenty-seven children and adolescents diagnosed with ADHD took part in the study, and their brains were compared with those of 46 healthy counterparts.

Previous studies have suggested that there is a small reduction in brain volume, of between 3 and 5 per cent, among children with ADHD compared with their counterparts.

But this is the first large-scale research to use magnetic resonance imaging (MRI) scanners to get an idea as to where, more precisely, the problem may lie.

ADHD is a recently-defined neuropsychiatric disorder.

Children with it have trouble concentrating, keeping still and observing discipline, and often as a result do very poorly at school.

Between 3 and 6 per cent of American schoolchildren have this condition, according to the authors, led by Elizabeth Sowell, assistant professor of neurology at the University of California, Los Angeles.

The cause of ADHD is unclear, but the frequent method of treatment is psychostimulants, a class of powerful drugs that is a stimulant in adults but in children has a calming effect.

These medications can also have big side effects.

One of the useful consequences of the latest research would be to fine-tune these drugs so that they can specifically target affected parts of the brain, said co-author Bradley Peterson, a professor of psychiatry at New York's Columbia University.